Bobbin-thread tension-device for sewing machines



Sept-.27, 1 932., I w. L. BARRON I 3 9,

3013mm THREAD TENSION DEVICE. FOR SEWING-MACHINES Filed July 29 195. A

swam atop H/z'liiam L. Barron.

Patented Sept. 27, 1932 a mare SAEES 'iT HCE WILLIAM L. BARRON, OF LAURENCE HARBOR, NEW JERSEY, ASSIGNOR TO THE SINGER IvIAI'IUFACTURING COMPANY, OF ELIZABETH, N EXV JERSEY, A CORPORATION OF NEW JERSEY BOBBIN-l'I-IREAD TENSION-DEVICE FOR SEWING MACHINES Application filed July 29, 1931. Serial No. 553,863.

This invention relates to bobbin-thread tension-devices for sewing machines and more particularly to such devices for sewing machines having a circularly moving looptaker or shuttle within the field of which is supported a thread-case for awound mass or bobbin of thread.

In the use of a sewing machine for certain ornamental stitching and embroidering op erations, it is necessary to run the bobbin- 'thread under a heavier tension than is ordinarily required in regular straightaway sew- .ing operations. For example, in embroidery cording or cord-covering operations, a heavy bobbin-thread tension is required to insure the proper tightness of the stitches around the cord or filler-thread used. In other cases, a heavy bobbin-thread tension is required to insure that the lock-points of the needle and 0 bobbin-threads will not be drawn through to the upper or finished side of the work'by the sewing machine take-up. Furthermore, it is often desirable to run these comparatively heavy tensions on very fine threads of, say from .0025 to .005 inch in diameter.

It has been proposed to meet the require ments for embroidery work by increasing the thickness of the usual bobbin-thread tension spring but this has proven unsatisfactory as the increased thickness so stiffened the spring that it would not readily permit the passage of lumps or irregularities in the bobbinthread and would not impose a uniform tension on the thread with a satisfactory degree of certainty. A slight increase or decrease in the size of the thread, for example, would cause a great variation in the tension and spoil the appearance of the work.

For other sewing operations a light bobbinor under-thread tension is required and where a heavy enough spring was used to meet embroidering requirements it was found impossible to adjust it to a light uniform tension on the thread desired for other sewing operations.

The present invention, therefore, has for an object to provide a bobbin-thread-case of the circular type with a tension-device hav- 7 ing a wide range of adjustment to adapt the 50 machine for a great variety of sewing opera taining uniformity of action of the device under any given adjustment. Still further, the invention has for an object to provide a bobbin-thread tension-device meeting these requirements while preserving a minimum working clearance between the thread-case and the loop-taker or shuttle.

To the attainment of the ends in view, the invention comprises the devices, combinations and arrangements of parts hereinafter describedand claimed. r

The features of the invention and the advantages attained thereby will be readily understood by those skilled in the art from the following detailed description of a preferred embodiment of the invention illustrated in the accompanying drawing, in which Fig. 1 is a front face elevation of a bobbin-threadcase embodying the invention. Figs. 2 and 3 are enlarged sectional views of the threadcase showing the tension-spring adjusted for light and heavy tension requirements, respectively. Fig. 4 is a top plan view of the thread-case in working position and Fig. 5 is a disassembled perspective view of the thread-case.

1 represents the usual sewing machine throat-plate having the needle-hole 2 and feed-dog slot 3. Disposed below the throatplate 1 is the circularly moving loop-taker 4c illustrated in the form of the usual oscillatory shuttle having the raceway-bearingrib 5, the loop-seizing beak 6 and the throat 7 and heel 8 which are engaged by the usual shuttle-driver (not shown). The shuttle is shownin one extremeposition of its oscila slot 14: in which is anchored the tail end 15 of the leaf tension-spring 16 which is made from fiat spring stock bent to the curved form shown and hardened and set to have an unsprung radius of curvature less than the radius of curvature of the outer surface of the thread-case. It isnot to be understood that the unsprung curvature of the spring 16 is in the true are of a circle throughout its length. The point is that it is more sharply arched than the surface of the thread-case to which it is applied so that it tends to engage the surface of the threadcase at its extreme ends and is arched up between its ends where it is formed with a clearance hole 17 for the tension-adjusting screw 18 threaded into the aperture 19 in the thread-case.

The end of the tension-s ring 16 opposite or remote from the tail en 15 is preferably formed to constitute a bobbin-thread delivery-guide; such end preferably having ear-portions 20 bent over upon the exposed or outer face of the thread-case and received in the face-notch 21 in the thread-case; such ear-portions being preferably formed with or defining a thread-delivery aperture 22.

The bobbin-thread 13 leads from the bobbin 12 outwardly through the thread aperture 23 to the outer surface of the thread-case over which it runs under the spring 16 to the thread-guide 22 and is pressed upon by the spring 16 only at the point 24 considered circumferentially of the thread-case, as shown in Figs. 2 and 3.

It will be observed that the extreme end 25 of the spring 16 is free of interference with the thread-case under all conditions of ad justment of the curvature or tension of the spring 16 within the limits provided. This objectionable end-contact is avoided preferably by flattening the outer cylindrical surface of the thread-case, as at 26. The only point of thread-tension contact is definitely fixed at the point of intersection 2 1 between the flat 26 and the outer circular wall of the thread-case, and remains fixed under all conditions of adjustment and variations in ourvature of the spring 16 caused by its adjustment without interference between the extreme end of the spring and the wall of the thread-case.

7 By virtue of the present improvement a spring 16 of desired flexibility and strength may be so set or initially curved to gain the desired heavy tension when strained to the position of adjustment shown in Fig. 3, and still permit a uniform weak-tension to be attained by backing off the screw 18, Fig. 2, without danger of interference with the pressure upon the thread by engagement of the extreme end 25 of the spring 16 with the thread-case. Thus, under all conditions of adjustment, the entire pressure of the tension-spring is applied to the thread at a definite point, regardless of the degree of deformation or arching of the tension-spring caused by the adjusting screw 18. A spring of considerable flexibility may be used to good advantage, giving a wide range of tension adjustments with a high degree of uniformity of action for any given adjustment.

Having thus set forth the nature of the invention, what I claim herein is 1. A bobbin-thread-case having a circular shell and a thread-tension leaf-spring applied to the outer surface of said shell, said spring having an unsprung radius of curvature less than the radius of curvature of said surface, a tension-adjusting screw passing through said spring between the ends of the latter and into said shell, the proximate surfaces of said spring and shell adjacent one end of said spring being shaped to provide a definite and fixed point of contact between the two circumferentially of the thread-case and Within said end of said spring for any adjustment of the tension and curvature of said spring within the working limits provided, the extreme end of said spring adjacent said point of contact being free of interference with the threadcase under all conditions of adjustment.

2. A bobbin-threadcase having a circular shell and a thread-tension leaf-spring applied to the outer surface of said shell, said spring having an unsprung radius of curvature less than the radius of curvature of said surface, a tension-adjusting screw passing through said spring between'the ends of the latterand into said shell, the portion of the threadcase under one end of said spring being flattened to permit free tilting movement of said end and to prevent contact between said end and the thread-case for any adjustment of the tension and curvature of said spring within the working limits provided.

In testimony whereof I have signed my name to this specification. 

